The objective is to determine the process affecting cellular repair of DNA and their effects on radiation responses of cells, particularly solar ultraviolet radiation. Attention is focussed on processes induced by radiation damage, and the factors which modify these cellualr reactions. Specific aims involve characterization of enhanced DNA repairs induced by UV light exposure in mammalian cells, regulation of the gene for DNA photolyase in E. coli (producing the enzyme responsible for photoenzymatic repair of pyrimidine dimers in DNA), and clonong of the photolyase gene from a marsupial cell.